The problem is probably not with PLEX but with Chinese devices people buy which do not have any codec support due to the licenses plus wrong implementation of public audio standards.
Get yourself proper device with licensed codecs like Sony or Philips TV, FireTV stick or nVidia Shield or post logs here for every problem you have because without it nobody can tell what issues you are really facing.
Easy for Plex – classic response (even though they state it is a multi-platform software). If people are buying and using these boxes than it is incumbent on Plex to develop a solution if they wish to continue in business.
If everybody is using these boxes, people will just migrate to Kodi (free) vs Plex Pass ($). Multi-platform software should never dictate what hardware you have to buy and if it does … run away!
Did this ever get resolved? I have the same issue with 2 different brand new android boxes.
A Vorke Z6 Plus and an H96 Pro +. I have Plex Pass but perhaps not for much longer.
Sound works in Kodi and Kodi Plex addon.
Does not work in native Plex for Android.
Both running android 7.12 and Plex is up to date.
Both connected via HDMI to TV and TV has optical to Samsung sound bar.